Controversy regarding genetically modified (GM) plants and their
potential impact on human health contrasts with the tacit acceptance
of other plants that were also modified, but not considered
as GM products (e.g., varieties raised through conventional breeding
such as mutagenesis). What is beyond the phenotype of these
improved plants? Should mutagenized plants be treated differently
from transgenics? We have evaluated the extent of transcriptome
modification occurring during rice improvement
through transgenesis versus mutation breeding. We used oligonucleotide
microarrays to analyze gene expression in four different
pools of four types of rice plants and respective controls: (i) a
gamma-irradiated stable mutant, (ii) the M1 generation of a 100-Gy
gamma-irradiated plant, (iii) a stable transgenic plant obtained for
production of an anticancer antibody, and (iv) the T1 generation of
a transgenic plant produced aiming for abiotic stress improvement,
and all of the unmodified original genotypes as controls. We found
that the improvement of a plant variety through the acquisition of
a new desired trait, using either mutagenesis or transgenesis, may
cause stress and thus lead to an altered expression of untargeted
genes. In all of the cases studied, the observed alteration was more
extensive in mutagenized than in transgenic plants. We propose
that the safety assessment of improved plant varieties should be
carried out on a case-by-case basis and not simply restricted to
foods obtained through genetic engineering.